1. Field of the Invention
The present invention relates to connections to an electrical distribution grid, and in particular, to a converter topology for interfacing a load with the grid.
2. Background of the Related Art
Connection of large power generators and power loads to electric distribution grids calls for robust power converters capable of handling a variety of situations. For example, in high power applications such as where compressor drives and large wind turbines are connected to the grid, the power converter between the variable-speed machine and the grid should ensure high power quality both at a machine interface and at a grid interface. It is desirable that output from the power converter for connection of either one of the load and the supply provide three-phase power at medium voltage levels.
High power medium voltage power converters for industrial applications typically use different multilevel topologies. Popular examples of industrial power converters include power converters having a neutral point clamped (NPC) topology, a flying capacitor topology (FC) and an H-bridge series cell topology (HSC). The NPC and FC topologies present complexity in design and implementation beyond three-levels. Hence practical implementations of the NPC and the FC topologies for high power are usually limited to three level configurations—thus the output power quality is limited in some instances. The HSC topology can be scaled to high powers at high power quality; however, the HSC topology similarly calls for a transformer arrangement that is complex when scaled to high powers.
What is needed is a topology that can be scaled to higher powers and simultaneously can be designed for redundant mode of operation to increase availability. As the frequency for a coupled supply or load can vary over a wide range, the converter topology should be generic and provide for use in a variety of different applications.